1. Field of the Invention
The present application discloses a method and an apparatus for causing excitation of turbo-machinery blades that reproduces the vibrational effects of stator wakes and other turbulent airflow. The method and apparatus comprise generating eddy currents in the blades by an array of magnets to produce appropriate forces.
2. Description of the Related Art
Avoidance of fatigue failure is a major factor in turbo-machinery maintenance and replacement. High-cycle fatigue results from resonant modes in the rotor blades and synchronous excitation of such resonant modes. The turbulent wakes trailing from stator vanes are a leading cause of blade vibration. FIG. 1 illustrates the relation between upstream stators and turbine blades in turbo-machinery. Stator vanes create turbulent wakes that cause vibration in turbine blades. In order to study such effects, blade vibration must be reproduced in an evacuated test facility. FIG. 2 illustrates the evacuated spin pit in which blade vibration is to be reproduced.
In order to stimulate the modes of vibration experienced in turbines, an appropriate means of excitation is required. Several methods have been used or proposed. They include air jets, electromagnets operating on ferro-magnetic blades or ferro-magnetic patches of material, piezo-ceramic patches, vibration of the entire hub-blade system, and fluid jets. FIG. 3 illustrates these alternatives, and also notes the deficiencies of each one.
The present application discloses a method and an apparatus for causing excitation of turbo-machinery blades that reproduces the vibrational effects of stator wakes and other inhomogeneous airflow. The method comprises positioning an array of magnets near turbo-machinery blades to generate eddy currents in the blades to produce appropriate forces.
In preferred embodiments of the method, the magnets are positioned so as to obtain periodic vibration of the blades equivalent to that from stator wakes; the array of magnets are configured to appropriately phase an excitation force applied to various portions of the blades such that a particular target mode of vibration is strongly excited; the magnets are repositioned relative to passing blades to control the excitation force; and the array of magnets is designed with reference to a computational model of an unsteady magnetic interaction.
The apparatus for causing excitation of turbo-machinery blades that reproduces the vibrational effects of stator wakes and other inhomogeneous airflow comprises means for generating eddy currents in the blades by an array of magnets to produce appropriate forces.
In preferred embodiments of the apparatus, the magnets are positioned so as to obtain periodic vibration of the blades equivalent to that from stator wakes; the array of magnets are configured to appropriately phase an excitation force applied to various portions of the blades such that a particular target mode of vibration is strongly excited; the magnets are repositioned relative to passing blades to control the excitation force; and the array of magnets is designed with reference to a computational model of an unsteady magnetic interaction.